1. Field of Use
This invention relates generally to hydraulic control systems for elevating or self-loading scrapers and, particularly, to such systems for operating the bowl lift cylinders, the elevator lift cylinders and the ejector cylinders of such scrapers.
2. Description of the Prior Art
Some elevating scrapers employ a bowl open at its forward end, bowl lift cylinders for raising and lowering the front end of the bowl, a motor driven elevator at the open end of the bowl for loading the bowl, elevator lift cylinders for raising and lowering the elevator relative to the forward cutting edge of the bowl, and ejector for unloading the bowl by pushing material out through the open end of the bowl and ejector cylinders for moving the ejector between retracted (rearward) and eject (forward) position. In some such prior art elevating scrapers, uncoordinated operator use of the controls for the bowl, elevator and ejector can have undersirable results. For example, ejection of material by the ejector directly against an elevator in lowered position can result in damage to the elevator. Furthermore, lowering of the bowl to effect a deeper cut without raising the elevator above the cutting edge to compensate for the increased load of material can overload or also physically damage the elevator. The prior art discloses several hydraulic control systems for elevating scrapers aimed at overcoming these and other related problems and the following U.S. patents are exemplary: U.S. Pat. No. Re. 26,398; U.S. Pat. Nos. 3,653,132; 3,386,344; 3,296,716; 3,346,972; 3,484,960; 3,581,415; and 3,258,926.